Semiconductor product manufacturers must continually improve the power and performance of semiconductor devices while keeping the device size to a minimum. A common way to achieve a smaller device is to simply shrink the dimensions. Another widely practiced method of keeping the semiconductor device size to a minimum is achieved by designing and fabricating devices having multiple conductive layers. This is apparent in double-level and triple-level polysilicon and metallization processes.
Manufacturing difficulties have arisen with these complex processes. For example, with smaller and smaller geometries, alignment tolerances in photolithography operations have been significantly reduced. Another difficulty with fabricating multi-layer devices is that of planarizing the various layers. Several known planarization techniques and disadvantages with the techniques are described in the background of the above cited co-pending patent application, Ser. No. 07/546,801. The co-pending application teaches how to selectively planarize a semiconductor device, in other words, how to planarize only areas of the device in which contacts are not to be formed. With the selective planarization process disclosed in the co-pending application, a self-aligned contact is formed and the device is planarized without having to etch overly thick insulating layers.
Another common semiconductor device fabrication problem is the guaranteeing of electrical isolation of a self-aligned contact from underlying conductive members. While etching an insulating layer of the device, sidewall spacers are often formed along conductive members to provide electrical isolation. However, in order to completely etch the insulating material from an area in which a contact is to be formed, the integrity of the sidewall spacers is typically difficult to maintain during the etch process. Sidewall spacers are also attacked during subsequent cleaning steps. Without adequate isolation, the conductive members may be electrically shorted to other conductive members, for instance a contact, possibly causing the device to fail.